This invention relates to a motor drive unit for an electric motor operated vehicle and more particularly to an improved, compact motor and reduction transmission unit for driving the hub of a vehicle wheel.
There is an increasing demand for the use of electric power driven or electric power assist, manually-driven vehicles. These vehicles may take many forms but bicycles are a common utilization of this type of vehicle propulsion system. It is important that the motor and its driving transmission can be compact so as to facilitate the utilization of the electric motor and transmission with generally conventional-type vehicles.
Ideally, the motor and transmission could be assembled as a part of the hub of a driving wheel for the vehicle. This gives rise to considerable problems in providing both a compact arrangement and also one which will have a high enough speed reduction to make its utilization in an in-the-hub mounting practical.
It has been proposed to provide a unit wherein the electric motor has its output shaft generally tubular in nature and journaled around a fixed axle of the drive unit. This then drives the hub of the motor transmission unit through a two-stage planetary gear reduction transmission. The gears of the transmission also are disposed around this fixed axle shaft. As a result, the construction becomes quite large.
Part of the size increase is due to the fact that the transmission must provide a fairly substantial step-down in the ratio of speed between the output shaft of the electric motor and the driven hub of the wheel. This is one reason why a two-stage planetary reduction gear is employed. Nevertheless, because the transmission must encircle the fixed axle, the overall size becomes unacceptably large.
It is, therefore, a principal object of this invention to provide an improved electric motor reduction gear transmission drive assembly for the hub of a driven wheel of a vehicle.
It is a further object of this invention to provide a compact motor step-down transmission for such a purpose that can be utilized within the hub of a generally conventional wheel and which can be mounted on a generally conventional vehicle in the manner that a non-driven wheel is mounted.
Aside from these difficulties, there is also the problem of noise generated by the large gear reductions provided through the two planetary transmissions. Because of the fact that the gears are quite large and because of the high reduction ratio, noise is a constant problem with the prior art type constructions, particularly those mentioned above.
It is, therefore, a still further object of this invention to provide an improved step-down transmission for an electric motor driven vehicle wheel hub.
It is a further object of this invention to provide a two-stage planetary gear reduction unit for a transmission that incorporates a frictional transmission in its primary stage so as to reduce size and noise without diminishing the torque transmitting capabilities of the transmission.
In addition to the problems already noted in connection with the making of a compact motor reduction gear transmission for driving the hub of a vehicle wheel, there is additionally the problem of transmitting the electrical power to the motor for controlling its operation. Frequently, these types of motors are utilized in drive systems where there is also, as previously noted, primarily manual propulsion for the vehicle. Many of these arrangements employ controls that sense the amount of manual power input and then provide an electric motor assist in proportion to the amount of manual power applied for driving the vehicle. Various control strategies and relationships between input power, vehicle speed and other factors are employed for this control.
Nevertheless, it is necessary to transmit both electrical power from a storage battery or other electric power source and control signals to the motor for its operation. This provides additional problems in connection with maintaining a small size and also in reducing the number of electrical components that must pass through the housing to the motor and drive unit.
It is, therefore, a still further object of this invention to provide an improved and compact electric motor and reduction unit for driving a vehicle wheel hub and which incorporates a simplified and effective electric supply arrangement for transmitting electrical power to the motor.